Background: In Canada, the recommendation is to offer PPV23 at age 65 years. PCV13 is now licensed for adults. In Quebec, PCV7 was used in the immunization program for children in 2005-2008, PCV10 in 2009-2010 and PCV13 starting in 2011.

Methods: IPD cases reported to public health authorities and characterized by the provincial reference laboratory in 2000-2014 were analyzed. Age- and serotype-specific IPD yearly rates were adjusted for improvement in reporting and serotype identification. Time-series forecasting (SAS Software) was performed using log linear or logit transformation of yearly rates (selected according to lowest mean absolute percentage error), taking baseline periods defined according to dates of introduction of different PCVs for children and up to 2014, and assuming different time horizons to reach a new equilibrium following herd effect and replacement.

Results: IPD rate (per 100 000 person-years) and serotype distribution in the age group 65-74 years.

Serotypes

Observed 2004

Observed 2014

Predicted* 2019

Predicted* 2024

PCV7 types

Rate

20.8

1.0

0.2

0.0

%

58.6

4.2

0.6

0.1

PCV13-PCV7-Sp3 types

Rate

3.0

3.7

1.3

0.5

%

8.6

16.1

5.0

1.3

Serotype 3

Rate

2.0

3.2

4.3

6.1

%

5.7

14.0

16.5

17.3

PPV23-PCV13 types

Rate

7.1

7.6

11.7

19.1

%

20.0

32.9

44.9

54.3

Non-vaccine types

Rate

2.5

7.6

8.6

9.5

%

7.2

32.9

32.9

26.9

All IPDs

Rate

35.5

23.1

26.1

35.1

Conclusion: Forecasting S. pneumoniae epidemiology should be made with great care but is a must for the economic analysis of adult vaccination. In the age group 65-74 years, IPD caused by PCV7 types has been decreasing during the 2004-2014 period and stabilization at low level is now observed. The same pattern is underway with PCV13/Non-PCV7 types, with the exception of serotype 3 seeming to increase. PPV23/Non-PCV13 types and Non-Vaccine types are on the rise since 2004 and their contribution to overall IPD incidence during the next decade will be determined by the time needed to reach a new equilibrium.